Optimizing Permittivity Grading in Power Semiconductor Modules to Reduce Electric Field Stress at the Triple Junction

One of the major concerns in high-voltage power semiconductor modules is the high electric field stress at the edge of the metallization, where the substrate, encapsulation material, and electrode meet; commonly referred to as the triple junction. If this stress is not controlled, partial discharge may occur, eventually leading to insulation failure. To mitigate this issue, electric field grading techniques, such as the use of permittivity-graded materials in encapsulation, have been investigated. However, the optimal distribution of permittivity remains unclear. This study explores the effective distribution of relative permittivity ($\varepsilon_{\mathrm{r}}$) in permittivity-graded materials for reducing electric field stress at the triple junction. By comparing the stress-reducing effects of four different types of permittivity distributions, the study aims to identify and discuss the most effective approach.